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Null coalescing: The null coalescing operator “??” uses two question marks. With it you can use a custom value for a null reference variable. It simplifies null tests.

C# program that uses null coalescing operator

using System;

class Program
{
    static string _name;

    /// <summary>
    /// Property with custom value when null.
    /// </summary>
    static string Name
    {
        get
        {
            return _name ?? "Default";
        }
        set
        {
            _name = value;
        }
    }

    static void Main()
    {
        Console.WriteLine(Name);
        Name = "Perls";
        Console.WriteLine(Name);
        Name = null;
        Console.WriteLine(Name);
    }
}

Output
-------
Default
Perls
Default

Null conditional: Similar to the coalescing operator, the null conditional operator tests for null before accessing a member of an instance.

C# program that uses null-conditional operator

using System;

class Program
{
    static void Test(string name)
    {
        // Use null-conditional operator.
        // ... If name is not null, check its Length property.
        if (name?.Length >= 3)
        {
            Console.WriteLine(true);
        }
    }

    static void Main()
    {
        Console.WriteLine(1);
        Test(null);
        Console.WriteLine(2);
        Test("cat"); // True.
        Test("x");
        Test("parrot"); // True.
    }
}

Output
-------
1
2
True
True